Okay. Here's how this works.

Polaris has the damage of a Storm Driver on an unexpanded shot. That's not what a user is going for; they're going to want to stay at a distance. Three Polaris shots on Depth 24 with no damage boost will cause 594 (198x3)damage, the same as two Nova Driver shots, to a single enemy. Polaris also has a respectable AOE on an expanded bullet, but has both knockback and Shock, making it relatively unpredictable as far as multiple AOE hits go, unless combined with walls, VT, or a Vortex. It won't instagib zombies, but the damage will add up; it's more like a grenade launcher than anything else. Its knockback can also be used for pushing enemies away before they attack; if Shock connects, all the better, because they won't attack anyway!

Nova Driver has the same damage as an expanded Polaris shot without shock. Its regular shots can ricochet twice allowing for 1188 damage in a single clip; however, you've gotta get close or have plenty of enemies to easily pull that off. Its shots also have a tiny AOE that might get an extra enemy with a single bullet. The charge attack is the main attraction, though; this big mean mother hubbard will sock an enemy with initially 383 damage in a small AOE (enough to hit three or maybe four baddies with good aim, but more likely just to hit two) and then spew out four ricocheting shots, allowing up to twelve hits for the same 198 damage per bullet. In the event that four shots connect (very likely in a group of like ten zombies) this is a total of 1175 damage. If eight shots connect, that's 1967 damage. If you sock two enemies with the charge bullet (possible with good aim) and get eight hits, that's 2350 damage. For the perfect 12 hits with 2 enemies hit by the charge bullet, you dish out 3142 damage- and this is easy if you can shoot right into the center of a zombie mob!

To keep up with that... let's say Polaris can get off two clips in the time it takes to charge and fire the Nova. That's six bullets, each bullet dishing out 198 damage. 3142/198=15.868686... So you'd need to connect 16 successful hits with the AOE of six bullets to match Nova's damage before factoring in Shock (which, if the enemies are close enough to the shocked victims, might push Polaris's damage over the edge). With an Electron Vortex around this is no problem. Without one, it's still doable if at least three targets are near each other and near a wall; a good example of this is in Charred Court in the circular room with the rotating fire bar, where the second wave of Slags is near the wall. Another thing; if you have both a Driver and a Polaris, and you're entering a battle room with a Party Button trigger, it may be better to charge the Driver (or a Blitz or Brandish) first, because then you can just fire it off as the wave begins.

Storm Driver does less damage, so it's easier for Polaris to outmatch before Shock is factored in; both have the same Shock rate and potency, so no difference on those lines. Hail Driver and Magma Driver, because of their status effects, are completely different tactical options (and Magma's probably not a great choice for FSC in the first place).

I'm gonna need numbers for how many Polaris shots can actually be fired in the time it takes to charge and fire a Nova Driver shot, as well as numbers for max damage on both. Keep in mind that this is Depth 23 I'm talking about; Nova gets a bit more edge on 28 because Charge damage gets slightly more of a boost, comparatively, than standard bullet damage, but not too much of one, so Polaris is still about as viable.

Just remember; think about how your Knockback will affect players, whether for good or ill.

If you can't switch and don't want to learn how, get a Polaris. The crowd control and anti-turret capability will be very handy, and it won't slow you down that much. If Polaris is too mainstream for you, look for CTR on an alchemer and use charged shots. If you learn how to place them well, they are probably about on par with Polaris.
If you want to be a gun pro and get RSI, get an alchemer with ASI and go at it. The reason Storm driver can easily match Polaris here is, you will fire faster, land more hits and ricochets. This actually works best with a group of enemies in tight spaces or close quarters, as your shots will bounce repeatedly and everything dies around the same time.
On a side note, you can also switch-shoot a Polaris, but unless you've got the target immobilized somehow most of those hits won't land. It does make a fun technique against devilites if your party doesn't mind though. Basically, you can saturation-bomb an area, and they will all die or be heavily damaged trying to dodge, and you can mop up with a fencing sword.